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Enterobacteria are bacilli that are typically 1-5 μm in length. They lack cytochrome C oxidase (except for Plesiomonas shigelloides). They are facultative anaerobes, fermenting sugars to produce lactic acid. Most of them reduce nitrate to nitrite; an exception to this is Photorhabdus species. Many of them have flagella as their locomotory organ. On blood agar, they appear as small grey colonies. They are non-spore-forming.

They are present in the lower part of the intestines of humans and other mammals. Examples of enterobacteria are species of the genera: Citrobacter, Cronobacter, Enterobacter, Escherichia (e.g. E. coli), Hafnia, Klebsiella, Pantoea, Plesiomonas, Proteus, Raoultella, Salmonella, Serratia, and Shigella. Many of them are nonpathogenic and are present in the normal flora of the gut of their hosts. However, they can become opportunists in immunocompromised hosts and some of them may bring disease such as when they contaminate food and then ingested by their host. For instance, certain strains of E.coli have been found to cause gastroenteritis, urinary tract infections, and neonatal meningitis. In order to identify to which genus they belong, microbiological techniques are carried out, such as the detection of deaminase production on phenylalanine agar, acetylmethylcarbinol production via VogesProskauer tests, catalase tests, oxidase tests, nutrient gelatin tests, etc.